1. Field of the Invention
This invention relates generally to motor control circuits, and more particularly to motor control circuits suitable for driving apparatus, such as, for example, rotary knives, in cyclical operations.
2. Prior Art
Various drive mechanisms for driving apparatus such as rotary knives and other apparatus are known. Among such systems are systems that utilize electrically or mechanically operated clutches that couple the device to be driven to a motor until the operating cycle of the device is completed, and then disengage the device from the motor, leaving the motor free running. In other systems, one or more solenoids are coupled to the device to be actuated and sequentially energized to provide the operating cycle. Still other systems utilize position sensing circuitry and speed sensing tachometers in conjunction with control circuitry responsive to the speed and position sensing circuitry to selectively apply energizing and braking voltage to the drive motor to provide the desired cyclical action. One such system is disclosed in U.S. Pat. No. 3,508,133.
While the above described prior art systems do provide a way to control the operation of a cyclically operating device, the systems employing clutches are prone to clutch wear and tend to put undue stress on the driving motor when the motor is engaged and disengaged. The systems employing solenoids tend to be complex and noisy in operation, and require a high peak current capability to operate the solenoids. Systems like the one disclosed in the aforesaid U.S. Pat. No. 3,508,133 do provide a relatively accurate way to control the position of a cyclically operating device, but such systems still require mechanical braking and clutches in order to operate properly.